The recent introduction of immunotherapy in clinical practice (Kantoff et al, Robert et al) emphasized the influence of immune responses on cancer prognosis and chemotherapy effectiveness. Among adaptive immune cells involved in antitumor responses, CD8 T cells (CTL) have been considered to be the main protagonists because they exhibit cytotoxic activity towards tumor cells expressing tumor associated antigens (TAAs). However, it is now clear that CD4 T helper 1 (Th1) lymphocytes also play a critical role in orchestrating the antitumor response. These cells, mainly characterized by INF-γ production, are critical for the induction and maintenance of CD8 T cells against tumors by providing help through multiple interactions (Shedlock et al). CD4 Th1 cells can also exert antitumor activity that is independent of CD8 T cells by recruiting and activating innate immune cell such as natural killers and macrophages (Kennedy et al, Perez-Diez et al). The IFN-γ secreted by CD4 Th1 cells also mediates direct antitumor or antiangiogenic effect (Street et al). A new dimension of CD4 Th1 cells role during cancer is also reported. It has been shown that CD4 T cells must pave the way for killer T-cell entry at tumor site (Bos et al) or infected mucosa (Nakanishi et al). Furthermore CD4 Th1 cells is required for the induction of cellular senescence and angiogenesis inhibition resulting in sustained tumor regression upon inactivation of the MYC or BCR-ABL oncogene in a mouse tumor model (Rakhra et al). In human, high density of tumor-infiltrating CD4 Th1 cells has been shown as good prognostic marker in colorectal cancer (Tosolini et al). Thus, stimulating CD4 Th1 cells is significant for improving antitumor responses. Despite recent progress indicating that pre-therapeutic immune parameters affect the efficacy of conventional chemotherapies (Fridman et al, Zitvogel et al), little is known about the relationship between tumor-specific CD4 Th1 immunity and efficacy of chemotherapy.
The CD4 Th cells recognize peptides of 15 to 20 amino acids presented by MHC class II molecules. MHC molecules in humans are normally referred to as HLA (Human Leucocyte Associated antigen) molecules. There are two principal classes of HLA molecules, HLA class I and HLA class II. HLA class I molecules primarily activate CD8+ cytotoxic T cells whereas HLA class II molecules primarily activate CD4 T cells. HLA class II molecules are encoded by 3 different subloci which are: HLA-DR, HLA-DQ and HLA-DP. However, CD4 T cell responses often described in cancer research are restricted to HLA class II molecule encoded by the HLA-DR sublocus. The identification of degenerate peptides of relevant TAAs able to bind to multiple HLA class II molecules may lead to improve cancer vaccine and to monitor CD4 T cell immunity. During the past years, different groups have focused on the identification of CD4 T cell epitopes from TAAs that could be used to improve anticancer immunotherapy. (Kobayashi et al, 2008, Campi et al, 2003, Kobayashi et al, 2000). However, the identification of HLA class II epitopes from TAAs is limited because of their important heterogeneicity. Indeed, the HLA class II locus is very polymorphic and have many variants, thus, finding peptides capable of binding multiple allelic variants of HLA-DR is a very hard work.
The telomerase protein has recently been the focus of attention for its supposed role in prevention of cellular ageing. Telomerase maintains telomere length in dividing cells and its over-expression is the predominant mechanism developed by malignant cells to escape telomere-dependent cell death (Martinez et al). Therefore, telomerase activity has been observed in all studied cancer forms, including stem cell-like tumor cells (Artandi et al) and is therefore a hallmark of cancer cells (Hanahan et al). Thus, telomerase seems to be a good prototype for universal TAAs. On this view, Telomerase-derived CD4 peptides could be very useful tools for developing immunotherapy in cancers.
International patent application WO 98/14593 discloses the amino acid sequence of human telomerase protein and also suggests the use of this protein and certain fragments thereof in active immunotherapy.
Schroers et al. have previously described TERT-derived promiscuous HLA-DR restricted peptides (Schroers et al, 2002 and 2003). However their role on cell-mediated tumor immunity was not completely addressed in preclinical models nor in a clinical setting. Recently, a cancer vaccine using a TERT-derived CD4 helper peptide was able to stimulate specific immune CD4 T immunity that could be related to an increased survival of cancer patients when combined with chemotherapy (Kyte et al, 2011; Schlapbach et al, 2011). Nevertheless, GV1001 vaccine also fails to induce specific immune responses and clinical benefit in other cancers (Scardino et al, 2002). Although this peptide is thought to congregate near CTL epitopes, the impact of GV1001-specific CD4 T cell help on antitumor CTL responses has not been investigated yet.